Methods and apparatuses for the detection of the blood pressure of a patient are well-known in the art. One type of apparatus involves the use of an invasive arterial line. In an arterial line device, a sensor is inserted into the artery of a patient. The signal from the arterial sensor is supplied to a patient monitor which calculates, among other parameters, the blood pressure of a patient. The patient monitor is also capable of sending a signal to the sensor to determine if the sensor is electrically connected to the patient monitor. Although such apparatuses provide continuous and accurate blood pressure data, there are many disadvantages. First, there is a potential risk of infection. Further, the procedure is costly and consumes valuable health care takers' time, in that it is a surgical procedure involving the insertion of a catheter into a patient's artery. In addition, the patient experiences discomfort.
In the area of non-invasive devices, one prior art teaches the automatic expansion of pressure cuffs and the measurement of the blood pressure based thereon. However, such devices can only be used intermittently. Prolonged and frequent use can lead to patient discomfort.
U.S. Pat. No. 4,669,485 teaches using two cuffs to measure the blood pressure of a patient. The absolute blood pressure of the patient is initially measured. Thereafter, the second cuff is maintained at a low pressure, continuously, to monitor continuously the relative blood pressure of the patient. In this manner, the blood pressure of the patient can be continuously monitored. However, such a device still involves using blood pressure cuffs, which can be a source of discomfort to the patient and the device is subject to patient motion and as a consequence degraded results.
In column 4, lines 39--column 5, line 3 of U.S. Pat. No. 4,669,485, reference is made to yet another prior art non-invasive device which measured the arterial wall displacement and used those measurements to determine the relative blood pressure. However, the use of only the displacement measurement is subject to error.
Reference is also made to U.S. Pat. No. 3,318,303. In that reference, the output of an external microphone sensor is used to determine the blood pressure of a patient. In particular, the so-called "Korotkoff" sound may be determined.
U.S. Pat. No. 4,203,451 discloses that a data processor can be used to receive signals from the Carotid transducer.
U.S. Pat. No. 3,773,033 discloses the use of an arterial vibration sensor to monitor the performance of the heart and arteries during a succession of cardiac cycles. However, a pressure cuff also applies variable pressure to a specified artery being monitored by the arterial vibration sensor.
Heretofore, none of the prior art devices or references has suggested a non-invasive apparatus for continuously and accurately measuring the blood pressure of a patient using data obtained from the arterial wall, thereby providing for greater patient comfort. Further, none of the prior art devices has checked for the integrity of the sensor, apart from it being merely electrically connected to the monitor.